Abstract:
In response to challenges such as low permeability (0.006×10
−15−0.066×10
−15 m
2), high breakdown pressures (up to 52.8 MPa), and difficult in fracture propagation in deep coalbed methane reservoirs of Jixi Basin, a novel CO
2 pre-enhanced fracturing technology is innovatively proposed based on engineering practices from Well Heijidi-2. This technology utilizes the cryogenic effect and chemical dissolution enhancement of liquefied CO
2 to significantly reduce the breakdown pressures of coal matrices, reactivate natural fracture networks, and create multi-scale complex fracture networks. Furthermore, utilizing the adsorption-displacement mechanism of supercritical CO
2, it enhances coalbed methane desorption efficiency. The volumetric expansion during phase transition also boosts reservoir energy, achieving highly efficient fracturing fluid flowback. The implementation employs a combined process of “liquefied CO
2-enhanced fracturing + active water proppant transport for fracture conductivity”. This involves staged injection of 101.4−113.3 tons of liquefied CO
2 per target layer, integrated with ball-sealing staged fracturing (using 50−52 temporary diverting balls) and multi-size quartz sand proppant placement. This methodology constructs a fracture system characterized by “high-conductivity near-wellbore fractures and fully-supported far-field fractures”. Microseismic monitoring revealed that the generated complex fracture networks were oriented east-west and northeast. Individual layers exhibited fracture lengths of 400−431 m, heights of 75−110 m, and network widths of 168−173 m. The cumulative gas production from coal groups C14+C13 and C16 reached 156 131 m
3, with a peak daily gas output of 1 145 m
3. Field results demonstrate that CO
2 pre-enhanced fracturing overcomes the bottleneck in low-permeability and deep coalbed methane reservoirs (>2 000 m depth) through synergistic mechanisms of “physical breaking-chemical permeability enhancement-energy driven”. This provides both theoretical and technical foundations for efficient coalbed methane development in the Jixi Basin.